Fluid catalytic cracking of hydrocarbons

ABSTRACT

In a process for the fluidized catalytic cracking of hydrocarbon oils to gasolines in which a mixed fresh and recycle oil feed is contacted with catalyst in a reaction zone and catalyst is regenerated in a separate regeneration zone by contact with an oxygen-containing gas, the contact time of hydrocarbon and catalyst and the reaction temperature are adjusted according to the feed to produce a coke deposit on the catalyst such that a temperature of at least 620 DEG C. is maintained in the regeneration zone and the flow of oxygen into the regeneration zone is controlled responsive to the difference in temperature between the catalyst section and the gas outlet section of the regeneration zone to maintain a predetermined temperature difference, whereby the oxygen content of the outlet gas is minimized and after-burning (combustion of carbon monoxide) precluded.  The operating variables controlling coke deposition are fresh feed temperature, catalyst circulation rate, fresh feed to recycle oil ratio and space velocity.  The regeneration zone temperature is maintained at 620-677 DEG  C. and the gas outlet temperature generally not more than 14 DEG  C. higher.  At the high regeneration temperatures used this temperature difference gives an indication of the oxygen content of the flue gas and by trial and error the necessary difference is found and thereafter maintained corresponding to an oxygen content below 0.2%.

Dec. 15, 1964 J. B. PoHLENz FLUID CATALYTIC CRACKING OF HYDROCARBONSFiled June 29, 1962 A r TOR/Veys United States Patent O 3,161,583 FLUIDCATALYTHC CRACKING F HYDRGCARBONS n Jack B. Pohlenz, Arlington Heights,Ill., assigner to Umversal Oil Products Company, Des Plaines, lll., acorporation of Delaware Filed .lune 29, 1962, Ser. No. 266,271 3 Claims.(Cl. 208-164) The present invention is directed to an improved methodfor operating a fluid catalytic cracking unit and more specifically to amethod for effecting improved product yields from a hydrocarbon chargestream by operating to have an increased differential temperaturebetween the reaction and regeneration zones and to maintain a hightemperature level within the regeneration zone.

It has been conventional for design and operating engineers to designand to operate uid catalytic cracking units as heat balanced units. Inother words, with prior data and experience as a basis for the design ofthe unit, it was customary to estimate a gasoline yield and cokeproducing rate and then calculate to obtain a heat balance with aparticular combined feed ratio (which may be defined as the ratio of thecombined volume of fresh feed and recycle oil relative to the volume offresh feed) and/ or the combined feed temperature which would appear toprovide a Steadystate operation.

However, the error in such a design was the assumption that coke-make orcoke-yield, i.e., the weight percent of coke produced based upon freshhydrocarbon feed, was a function of conversion rather than catalystcirculation rate and catalyst residence time in the reaction zone. Thoseunits which were designed to operate at low conversion levels and hencelow coke rates were frequently short on heat so that feed heaters wereprovided to furnish the thermal requirements. High conversion units, onthe other hand, had the problem of too much cokemake for heat balancerequirements, so that recycle was provided as a cooling stream totransfer the excess heat into the main column where such heat could beused to regenerate steam. 1n other cases, catalyst'coolers were providedto preclude what was thought to be excessive regenerator temperatures.It was customary to operate regenerators below l150 F, on thepresumption that a higher temperature would reduce catalyst activity andprovide a short catalyst life.

It may also be pointed out in connection with the operation ofconventional fluidized cracking units, that various upsets in aso-called steady-state operation can occur, as for example, there may bea loss of the recycle stream, an upset in feed preheat to the reactor,or an upset involving a catalyst cooler or water spray system associatedwith the regenerator. In each case, it has been found that the units, asinstrumentized and controlled, will thermally stabilize themselves, eventhough product yields which follow may be far from optimum. There is theever present demand and necessity to obtain from cracking units amaximum throughput and optimum product yields,

and with improved control means being incorporated as a part of thepresent improved method of operation to prevent damage to the unit dueto afterburning (that is undesirable high temperature burning of carbonmonoxide to carbon dioxide within the light phase zone or flue gasoutlet of the regenerator), it has been found advantageous to varyoperating control means to establish and maintain higher temperaturelevels in the unit, regenerator temperature levels being in the 1l50 F.to l250 F. range, with the metallurgy of the regenerator system,including internals, governing the upper temperature limit.

It is therefore a principal object of the present' invention toaccomplish an improved continuous fluid catalytic cracking operationthrough effecting increased temperature 3,161,583 Patented Dec. 15, 1964ice differentials between the reactor and regenerator and a hightemperature level in the regeneration zone.

A further object of the invention is to provide that one or moreindependent operating variables are utilized in an integrated manner inthe lluidized unit' to insure a coke deposition on the catalyst whichwill result in an increased temperature spread between the contact zonesand a resulting regenerating zone temperature level at above about 1150F.

As is well known in the petroleum industry and as will be more fullypointed out hereinafter in connection with the accompanying diagrammaticdrawing, a conventional fluid catalytic cracking unit makes use of areactor, stripper, spent catalyst slide valve, regenerator, standpipe,regenerated catalyst slide valve, and a riser line leading back into thereactor, with the catalyst flowing through the various sections of theunit, in the order named. A large fractionator or main column is alsoutilized to receive the overhead cracked vaporous product stream fromthe reactor. Such fractionator provides gasoline and other desiredside-cut product streams therefrom, as well as recycle oil streams whichare charged back to the reaction zone. The mixture of fresh hydrocarbonfeed stream and recycle, referred to as combined feed, is vaporized uponcontacting heated regenerated catalyst particles at the base of theriser lineand effects the lifting of catalyst in the reactor. Thereactor products along with a minute quantity of entrained catalyst areintroduced into the main column where, of course, the products arefractionated into the various overhead and side-cut streams in accordwith their volatility.

Reactor temperature controls the regenerator slide valve to provide, inturn, variations in catalyst flow from the regenerator to the reactor.The spent catalyst valve, regulating catalyst flow from the reactor tothe regenerator, is operated by catalyst level control means in thereactor.

There are various independent control variables that will effect theconversion of a hydrocarbon gas oil stream and/or combined feed which isintroduced into the reaction zone. As used herein, the term conversionis dened as the volume percent of the feed which is converted tomaterials lighter than the light cycle oil as separated from the maincolumn, but corrected to take into account the amount of gasoline in thecharge stream, The actual weight ratio of catalyst to fresh feed flowrates is called the catalyst to oil ratio (C/O ratio) and is an.

important variable in controlling the severity of the cracking reaction.With a given hydrocarbon feed rate, an increased catalyst to oil ratioproduces an increased ow rate of catalyst through the reaction zone.Although less coke will be formed on each unit of catalyst in view of ashorter contact time in the reaction zone, the total coke rateincreases. On the other hand, an increased or decreased contact time4between the oil and catalyst can be accomplished by a change in thespace velocity (weight hourly space velocity being defined as the freshfeed rate in pounds per hour divided by the mass of catalyst within thereaction zone). Thus, a decrease in weight hourly space velocity meansthat a lesser quantity of oil is contacting a given quantity of catalystper hour, or for a given time, such that there is an increase inconversion by reason of a longer contact time with to the reaction zone.The feed preheat may be varied directly by the amount of heattransferred to the feed stream by an oil heater or heat exchanger, oralternatively, by the quantity and temperature of the recycle streamwhich is combined with the fresh feed stream to provide the combinedfeed ratio.

Important independent operating Variables may thus be considered thecombined feed ratio, the combined feed temperature, and space velocity,although, of course, other variables such as the reactor pressure andthe catalyst activity or quality will have an effect upon conversion.The catalyst circulation rate in the system may be readily varied,however, it is regulated responsive to a temperature controller in turnconnecting with the reaction zone, thus the circulation rate and thecatalyst oil ratio are dependent Variables in the operation of thecommercial fluidized units.

In a broad aspect the present invention provides that in a continuousprocess for cracking a hydrocarbon charge stream in the presence ofsubdivided catalyst particles wherein the hydrocarbon stream effects atluidized contacting of the particles in a confined reaction zone,conversion products are separated from the contacted particles,separated catalyst particles containing a coke deposit effect iluidizedcontacting of lan oxygen containing stream in a separate confinedregeneration zone, combustion gas products are separated fromregenerated catalyst particles and such regenerated catalyst particleswith a reduced coke content are returned to the reaction zone forcontact with hydrocarbon charge stream, the improved method of effectingoptimum product yields from the hydrocarbon charge stream by operatingat a high temperature level in the regeneration zone, which comprises,varying the reaction zone temperature and the contact time of thehydrocarbon stream with the catalyst therein responsive to therefractory characteristics of said hydrocarbon charge stream andeffecting a coke deposition on the catalyst particles providing atemperature above about 1150 F. in the regeneration zone when oxidizingthe coke on the catalyst particles in the presence of a controlledoxygen containing stream introduced to such regeneration zone, with theintroduction of such oxygen containing stream being regulated directlyresponsive to a predetermined temperature differential between the gasoutlet section and the catalyst contacting section of the regenerationzone to minimize excess oxygen therein and to preclude excessive anduncontrolled afterburning in the upper portion of the regenerating zone.

In a more specific embodiment, the improved method of effecting superiorproduct distribution from a hydrocarbon charge stream comprises,increasing the preheat temperature of the fresh feed stream to in turnprovide an increased fresh feed temperature while reducing catalystcirculation rate, and to effect an increased temperature spread betweenthe reaction and regeneration zones, such that the temperature level inthe regeneration zone is above about 1150 F. and up to the metallurgicallimits thereof as the regeneration zone oxidizes the coke on thecatalyst particles in the presence of a controlled oxygen containingstream introduced into the regeneration zone.

In still another specific embodiment, the improved method of effectingimproved hydrocarbon product yields when operating at a highertemperature level in the regenerator may comprise, for a given freshfeed charge rate and temperature level, varying the combined feed ratioof fresh feed to recycle oils to increase the heavy oil content thereofand simultaneously increasing the reactor temperature and a temperaturedifferential between the reactor and regenerator and a coke depositionon the catalyst particles providing a resulting temperature above about1150 F. upon oxidizing the coke on such particles in the presence of acontrolled oxygen containing stream being introduced into theregeneration zone.

It should be pointed out, however, when one considers operatingvariablesto increase the temperature spread between the contact zones, and theregeneration temperature, or cracking severity, etc., that it is notsufficient to just make a change which alters conversion, since theimportant aspect of the present improved method of operating a fluidizedsystem includes effecting the desired product distribution at the sameconversion. For example, a high severity operation with a small amountof recycle being used, will actually provide a lesser quantity ofgasoline, due to the cracking of the gasoline into light gases in thereaction zone. For example, one can hold conversion constant, decreasecoke-make and improve product yields, or one may increase conversion andhold the coke-make constant and effect improved product yields. The termimproved product yields as used herein, means greater economic yieldfrom the charge stream by reason of increasing the yield of gasoline andlighter materials which have more marketability.

In order to more easily refer to the operation of a iiuid catalyticcracking unit and the operating variables in connection therewith,reference is made to the accompanying diagrammatic drawing and thefollowing description thereof.

Fresh hydrocarbon feed passes through line 1 and control valve 2 to apump 3 that in turn discharges into line 4 connecting with a feedpreheater 5. The latter provides a predetermined or controlled variablepreheatin g to the feed stream and passes it to the lower end of riserline 6 where heated catalyst particles combine therewith from standpipe7, having control valve 8, such that a resulting vapor-catalyst mixturerises in an ascending fluidized column to the lower end of the reactor9. In the reactor 9, further uidized contacting between the vaporousfeed stream and the catalyst particles will take place in a relativelydense fluidized bed 10 within the lower portion of the chamber, althougha major portion of the necessary cracking and contact with catalystparticles takes place in the riser line 6 such that a shallow bed or lowdense phase level of catalyst is utilized in chamber 9. Catalyst in anoil slurry may be combined with the fresh feed stream in the riser line6 from line 11 having control valve 12, while in addition, recycle oilmay be combined therewith by way of line 13 having control valve 14. Ashereinbefore noted, the combined feed ratio will vary in accordance withthe amount of recycle oils combined with the fresh feed stream to beintroduced into the reaction zone.

At the upper end of the reactor 9, the catalyst particles are separatedfrom the vaporous cracked reaction products by centrifugal separatingmeans 15 and then transferred overhead by line 16 to the lower end ofthe fractionator or main column 17. Separated catalyst particles fromthe light phase zone in the top of the reactor 9 are returned to thedense phase bed 10 by a suitable dip-leg 1S and resulting catalystparticles with a coke deposition and occluded hyrocarbons settle fromthe lower portion of reactor 9 into a stripping section 19 such thatthey may pass concurrently to a stripping gas stream introduced throughline Z0 having valve 21. Steam, nitrogen or other substantially inertgaseous stripping medium may be utilized in the stripping section toeffect the removal of absorbed and occluded hydrocarbon vaporouscomponents. Resulting stripped and coked catalyst particles move fromthe lower portion of stripping section 19 into the standpipe 22, havingcontrol valve 23, such that they may be transferred at a controlled rateto the regenerator 24.

In lthe regenerating chamber 24 the carbonizcd catalyst particles aresubjected to oxidation and carbon removal in the presence of air beingintroduced by way of distribution grid 25. The oxidizing air streamenters the regenerator by way of line 26, Valve 27, and blower 28, whichin turn connects by way of line 29 to air heater 30. In the presentembodiment, the blower is indicated as connecting directly with thelower end of the regenerator 24 and the pipe grid distributor 25. Theair heater 30 is utilized only to heat the air during the initialstart-up procedure. A bypass line 31, having control valve 32, connectswith the air line 29 in order to vent a portion of the air stream beingintroduced to the system from blower 28 and 'thus regulate the quantityof air actually being introduced into the lower end of the regenerator24, as will be more fully described hereinafter.

In the lower portion of the regenerator 24,Y a iluidized dense phase bed33 provides for hindered settling contact between the coked catalystparticles and -the oxidizing air stream while, in the upper portion ofthe chamber, a light phase zone permits the separation of catalystparticles from the flue gas stream being discharged by way of line 34and valve 3S. Suitable centrifugal separating means 36 provides forremoving entrained catalyst particles from the combustion product streamand returns them by way of dip-leg 37 to the lower dense phase bed 33. Asuitable silencing means 38, connecting with line 35, serves to reducethe noise level of the combustion gas stream passing to -the outletstack 39.

. present drawing. In addition various side-cut and recycle streams maybe taken from the side of the fractionator 1'7 in accordance withdesired molecular weight products. A`

light recycle oil stream is indicated as being takenfrom column 16 byway of line 42 and side-cut accumulator 43. An overhead vapor returnline 44 returns uncondensed vapors from accumulator 43 to the maincolumn 17 while a condensed light oil fraction is .taken from the lowerend of the accumulator 43 by way 'of line`45, pump 46 and line 57 havingvalve 48.` Similarly, a heavier recycle oil stream may be taken from themain, column by way of line 49 and side-cut accumulatorv 50. Anuncondensed vapor stream may be returned to the main column by way ofline 51 while a condensed heavy oil fraction passes from the lower endof accumulator 50 by line 52, pump 53, and line S4 having valve 55.Suitable lines, not indicated in the present drawing, may be, utilizedto transfer the light and heavy recycle oil streams from lines'i47 and54 to the-recycle inlet line 13 which in turn connects `with catalystriser line 6, such that recycle oil may be `16, may be transferred byway of the lower outlet line 56, pump 57, and line 58 to a suitablecatalyst settling chamber 59. The settler 59 serves to provide asubstantially, particle free claried oil stream overhead by way` of line69 and valve 61, while at the same time effecting the return of thecatalyst containing slurry stream through control valve 12 to transferline 11 such that catalyst particles may be returned to the iluidizedbed by way of riser line 6. A line 62, with control valve 63, isutilized to pass a portion of the bottoms stream from the main column 17through a heat exchanger 64 such that heated oil may be returned by wayof line 65Ato the lower end of the main column 17 :and provide a heatsupply to such column.

In order to maintain control of the iuidized unit, controlinstrumentation means are associated with the reaction and regenerationzones to maintain-appropriate dense phase bed levels in such zones and acatalyst` circulation rate between such zones. At the reactor 9, a levelcontroller LC, with level indicating taps 66 and 67,

is connected with the side wall of the reactor. A control line 68 fromcontroller LC connects with the slide valve 23 in the contacted catalyststandpipe 22 and provides` means for maintaining a desired dense phasebed 19 level and quantity of catalyst in the lower portion of thereactor 9. Generally, the slide valve control means, such as used inconnection with slide valve 23, are pneumatic in opera-Y Ation such thatthe level control means LC may be of any conventional type suitable toregulate the pneumatic motor control means of the valve, althoughelectrical control and motor means may be used.

Within the upper portion of reactor 9, a temperature indicating means 69connects through control line 70 to a temperature controller TC andcontrol line 71 which in turn connects with an air piston or other motormeans providing for the vregulation of the slide valve 8 in theregenerated catalyst standpipe 7. Thus, la variable quantity of hotregenerated catalyst maybe withdrawn from standpipe 7 to pass into riserline 6 and enter the reactor chamber 9 in accordance with variations internvperature in the latter zone, as provided for by the temperaturesensitive means 69 and controller TC. A pressure sensitive means 72 isalso positioned in the upper portion of the reactor 9 while a separatepressure indicating means 73 is positioned in the upper portion` of theregenerator 24. Such indicating means are connective, through therespective lines 74 and 75, to a ditterential pressure regulator DPR inorder to provide means for maintaining a desired differential pressurebetween the two separate contacting zones. The diferential pressureregulator DPR connects through control line 76 with the control valve 35so as kto regulate the ilue gas ow through line 34 and in turn vary ltheinternal pressure within the upper portion of the regenerator 24,whereby a predetermined pressure difference may be maintained betweenthe reactor and the regenerator. Generally, the pressure diierentialbetween the two zones is ofthe order of about 6 p.s.i. and is necessaryto permit the maintenance of suitable pressure differentials acrossthe'slide valves in the two standpipe lines and a continuous circulationof catalyst Vparticles between two separate zones. Pressures in afluidized unit are, of course, relatively low, being generally belowabout 425 to 30 p.s.i. because of the large size of the vesselsinvolved. Pressure variation in the reactor may be an operating controlvariable, but because of structural and mechanical aspects, it ispreferable to utilize low pressures which are merely suliicient toinsure yadequate differentials land proper flow between various portionsof the uni-t.

An improvedcontrol means integrated in connection with high temperatureoperations and indicated inthe present diagrammatic embodiment, is theuse of a differential temperature control means between the dense phaseand light phase zones of regenerator 24 so as to regulate the quantityof air being introduced into the regeneration zone. Temperatureindicating means 77 and 7S, within the upper and lower portions of theregenerator 24, connect through the respective transmission lines 79 andS0 to a differential temperature controller DTC, which in turn connectsthrough control line 81 with the valve 32 in the air vent line 31. Thus,where the temperature -diierential between the upper yand lower portionof the regenerator exceeds a predetermined diierence, as set within thetemperature controller DTC, then valve 32`is :adjusted to bypass agreater portion 'of the air passing through line 29 and effect thereduction of air being introeduced by way of distributing grid 25 intothe lower portion of theregenerator. Persons famili-ar with theoperation of iluidized cracking units realize that uncontrolledafter-burning can be a major problem inasmuch as theV high temperatureresulting from the oxidation of fcarbon monoxide to carbon dioxide in adilute phase and the cyclone separators at the outlet of the regeneratormay -cause severe mechanical damage. In the prior operation tering orbreakage by thermal shock of the particles, and (2) its nullifyingeffect on feed preheat. Prior attempts to reduce the flow of the airstream and the introduction of oxygen into the regeneration zone hasrequired sensitive means for detecting small oxygen concentrations andadjustment of the air introduction rate, all of which has been difficultfrom the practicable aspects. In the present embodiment, where it isdesired to have cracking operations which maintain a high temperaturelevel in the regenerator, in other words, above about 1150 F., it is, ofcourse, desirable to have means for precluding the problems ofafter-burning. It has been found that a temperature rise above apredetermined temperature differential between the dense and dilutephases or between the dense phase and the flue gas outlet line is a verysensitive indicating means to show variations in the oxygen content ofthe gas leaving the dense phase itself. With this procedure,after-burning may be controlled such that the regenerator temperaturescan be maintained at a steadystate level. In practice, it has been foundthat from 1% to 2% of the air blower output may be vented land that atemperature rise, over and above the predetermined differential set inthe DTC may be utilized to control valve 32 and the vent rate throughline 31. At the present time, it is generally necessary to determine bytrial and error on any particular unit that temperature differential orrise which, when maintained constant, will regenerate the catalyst tolower the coke level on the catalyst to a desired lower level, generally0.3-0.4 weight percent, and maintain the oxygen concentration in theflue gas below 0.2%.

In order to evaluate the present improved operation, utilizing hightemperature levels in the system, one may consider two dierent chargestocks: an A stock which is of parat-linie base having a high K value,or characterization factor, and is low in metals and Conradson carbon;as well as B stock which has a low K value and is high in contaminants.In a fluid catalytic cracking unit being operated and controlled in amanner as hereinbefore set forth in reference to the accompanyingdrawing, with a combined ratio of 1.5, a weight hourly space velocityequal to 2.0, and fresh feed temperature at 400 F. to the reactor riserline, the reactor temperature being adjusted to provide a 65 volumepercent conversion to gasoline, then the resulting steady-stateoperation providesy a reactor temperature of 890 F., regeneratortemperature of 1100 F., and 7.7 weight percent of coke. With the stock Bbeing charged to the unit under the same conditions and with reactortemperature adjusted to provide a 65 volume percent conversion togasoline, there is found a reactor temperature of 915 F., a regeneratortemperature of 1200 F., and coke amounting to 8.3 weight percent. The0.6 weight percent difference in coke-make is due to sensible heat inthe reactor and/ or regenerator vapors.

From the foregoing figures it may be noted that the poorer charge stockB can be cracked in the conversion unit lat a high temperatureconversion level to give a relatively high 65 percent conversion andthere will be no problems in maintaining a steady-state operation aslong as the 1200 F. temperature in the regenerator is below the limitsof any metallurgical problems encoun- -tered in the regenerator sectionof the system. On the other hand, it becomes apparent that the chargestock A could be treated in the system to provide substantially greateryields of gasoline or light materials by effecting changes in theoperating variables so as to provide an increased regeneratortemperature of the order of 1200 F. In other words, there may beanincrease in the preheating of the feed stream, say to the order of 700F. rather than the 400 F. feed temperature, an increase in regeneratortemperature say of the order of 75 F. and provide a reduction incoke-make from about 7.7 to less than 5.5 weight percent; conversion ismaintained constant by increasing reactor temperature. The lesser amountof cokemake indicates an increased amount of gasoline and 8 lighterproducts. 'Ihe increased feed preheat and the increased regeneratortemperature level permits the regenerated catalyst slide valve to beclosed down and to lower the catalyst circulation rate in the system sothat actually catalyst enters the reaction Zone at a reduced rate and ahigher temperature with the resulting effect that there will be a longercontact time of the catalyst particles but a reduction in total carbondeposition due `to reduced catalyst circulation rate. The trade betweencoke-make and more valuable product yields effects a very desirableimprovement in the economics of the unit. It is also important to notethat a fluid catalytic cracking unit can be varied in its operation inaccordance with the refractory characteristics of the feed and, in fact,evaluate a particular charge stock in terms of reactor and regeneratortemperature levels such that with the better charge stocks it ispossible to consistently improve yields by operating to maintain a hightemperature level in the regenerator as long as the high temperaturelevel pre- -cludes metallurgical damage to the unit.

In another instance, a series of performance tests were conducted in auid catalytic cracking unit in a manner which illustrates the advantageof a high temperature level in the system and an increased temperaturedifferential between the reactor and regenerator zones. In theparticular performance tests, three different levels of feed preheatwere used, with conversion being maintained constant by adjustments inthe reactor temperature. Specifically, the raw oil introduction rate wasmaintained at 28,000 barrels per day, the combined feed ratio was heldconstant for each performance test at 2.30, and catalyst content in thereactor or weight hourly space velocity was held substantially constant.In addition, in order to maintain uniformity during :the tests asconsistent as possible, there wasl a constant crude mix maintained inthe charge to the feed preparation unit so that the raw oil feed ratewas consistent and levels in the receivers and reboilers were heldconstant. In a Test #1, the fresh feed was held to a temperature of 414F. to provide a combined feed temperature of 500 F. The resultingreactor temperature for 69.7 volume percent conversion was 871 F. andthe regenerator temperature ll48 F. The catalyst circulation rateleveled off at 4.5 X10-6 pounds per hour and coke-make was 9.4 Weightpercent. Debutanized gasoline was measured at 49.6 volume percent whileother product yields were determined to be in accordance with thequantities set forth in the following Table I, under the column headedTest #1.

In a Test #2, the fresh feed was preheated to a temperature of 568 F.such that the combined feed temperature was 567 F. and a resultingreactor temperature and regenerator temperature were respectively 881 F.and 1168 F. The catalyst circulation rate in this instance was 3.8 10fiwhile the coke-make rate was 8.6 weight percent. The debutanizedgasoline production was 50.1 Volume percent while other yields were inaccordance with the quantities shown in Table I, under the column headedTest (2).

In a Test #3, fresh feed was preheated to a temperature of 698 F. toprovide a combined feed temperature of 620 F. and resulting reactor andregenerator temperatures respectively 888 F. and V1185 F. The catalystcirculation rate was 3.3)(10*E pounds per hour and the coke-make 7.9weight percent. The debutanized gasoline was 51.2 volume percent whileother product yields were in accordance with the quantities set forth inthe column under Test #3 of Table I.

Referring specifically to the Test No. 3 and the data in Table I, thereis noted a delta T of 297 F. temperature, which is the differencebetween the reactor temperature and regenerator temperature, that ishigher than occurs in either of the other test operations. It may alsobe noted that there is a significantly greater gasoline yield in Test#3, together with less hydrogen production in the C3 and lighter gases,showing that there is lesser hydrogen and coke-make which results in theincrease of gasoline yield from the system. Actually, in the highesttemperature level operation for the regenerator, as shown in Test #3,there is an increased coke deposition on the individual catalystparticles as such, due to a longer contact time in the reactor, and theresulting higher temperature level in the regenerator due to theoxidation of the coke from the catalyst particles. However, by reason ofa substantially reduced catalyst circulation rate, the overall rate ofproducing coke is reduced in the system and the coke-make, as indicatedas weight percent of the feed, is a lower Value in Test #3, than in theother two tests.

By way of summary, it may be noted from Table I that the coke reductionin turn appears as gasoline product even though the reaction temperaturehas been raised.

The weight fraction of C4 and lighter components remain substantiallyconstant, but the C3 and C4 fractions decreased with a correspondingincrease in the C2 and lighter fractions.

The olen content of C3 and C4 fractions increase, with the largestchange being in the C4 fraction.

The isobutane content of the C4 paraftins remains substantiallyunchanged as well as the properties of the liquid product.

The foregoing tests indicated changes in the regenerator temperaturelevels and product yields by varying the feed preheat, however,` otherindependent control variables may be modied to raise regeneratortemperature to one just below the design maximum. For example, there maybe a decrease in the yield of the main column bottoms stream (indicatedin the drawing as the clarified oil stream passing by way of line 60),by recycling to the reactor a higher quantity of oil in the slurrybottoms stream, (such as the stream passing by way of line 11 to riser 6in the drawing).

In other words, any combination of control variables may be employed upto the regenerator temperature limit set by the metallurgical aspects ofthat portion of the unit, such that temperature may range up to theorder of 1250 F. High temperature, with good operating practices,provides no problem with catalyst sintering or deactivation and, infact, regenerator operation appears to improve with respect to moreuniform coke removal. Uncontrolled after-burning may be precluded at thehigh regeneration temperature levels by the hereinbefore describedsystem of utilizing a temperature dierential control means across theupper and lower portions of the regenerator chamber to effect thecontrol of the quantity of air being introduced into the dense phasezone of the regenerator. Temperature dilerential becomes a sensitivemeasure of the quanti-ty of oxygen present and by having insufficientoxygen present to permit the oxidation of carbon monoxide to carbondioxide in the light phase zone of the unit, there is proper control toprevent a temperature runaway. Generally, a temperature diierential of25 F. as a maximum will permit a differential temperature controller toregulate the proportion of air to the regenerator by adjustment of thevalve in the air vent line from the air blower, to in turn provide for asteady-state regenerator operation wh-ich will preclude afterburning andat the same time effect a suitable reduction in the coke level to lessthan 0.5 percent coke by weight and preferably to 0.3 to 0.4 percentresidual on the catalyst particles. Of equal importance, however,

`the oxygen content of flue gas remains 0.0-0.2 percent which reducesthe oxidation rate of cyclones.

The coke production rate and the catalyst circulation rate Varyinversely with the regenerator temperature, as, for example, a coolregenerator operating temperature at say ll F. results in a high cokerate for a given combined feed ratio and combined feed temperature.Stated another way, the coke rate opposes the direction in which theregenerator temperature moves, so that operations at high temperaturelevels in the regenerator are in the direction of improved productyields.

TABLE I Test #l Test #2 Test #3 Operating Conditions:

Fresh Feed Temp., F..- 414 568 698 Combined Feed Temp., 500 567 621 YCombined Feed Ratio. 2. 30 2. 30 2.30 Reactor Temperature, F-- 871 881888 Regenerator Temp., F 1, 148 1,168 1, 185

- T. F. (Temp. Dinerential Between Reactor and Regenerator) 277 287 297Reactor Pressure, p.s.i.g 15 l5 15 Apparent Conversion, VOL-Percent 69.7 69.7 69. 7

Corrected Conversion (385 F. 90%

Gasoline) 69.2 68. 9 69.6

Catalyst Circulation Rate, Lb./Hr.X10-0 4. 5 3. 8 3. 3 Product Yields:

C; and Lighter, Wt.-Percent 7. 6 7.8 9.1

Total C4 Fraction, Wt.-Percent 8. 8 8. 6 7. 7

Debutanized Gasoline, (385 F. 90%),

VOL-Percent 49. 6 50. 1 51. 2 Light Cycle Oil, Vol.-Percent 26.1 27. 626. 7 Claried Slurry, VOL-Percent- 4. 2 3. 5 3. 7 Coke, Wt.-Percent 9. 48.6 7. 9

C3 and Lighter, Mole-Percent:

Total C4, L.V.Pcreent:

I claim as my invention:

l. In a continuous process for cracking a hydrocarbon charge stream in-the presence of subdivided catalyst particles, wherein the hydrocarbonstream eifects a uidized contacting of the particles in a confinedreaction zone, conversion products are separated from the contactedparticles, separated catalyst particles containing a coke deposit effectiuidized contacting of an oxygen containing stream in a separateconfined regeneration zone, combustion gas products are separated fromregenerated catalyst particles and such regenerated catalyst particleswith a reduced coke content are returned to the reaction zone forcontact with hydrocarbon charge stream, the improved method of effectingimproved product yields from the hydrocarbon charge stream by operatingto provide a high temperature level in the regeneration zone and anoverall reduction of coke yield in the process which comprises, varyingthe reaction zone temperature and the contact time of the hydrocarbonstream with the catalyst in the reaction zone responsive to therefractory characteristics of said hydrocarbon charge stream andeffecting a coke deposition on the catalyst particles suflicient toprovide a temperature above ll50 F. in the regeneration zone whenoxidizing the coke on the catalyst particles in the presence of acontrolled oxygen containing stream introduced to such regenerationzone, and regulating the introduction of the oxygen containing stream tothe regeneration zone directly responsive to a predetermined temperaturedifferential between the gas outlet section and the catalyst contactingsection of the regeneration zone to minimize excess oxygen therein andto preclude afterburning in the upper portion of the regenerating zone.

2. In a continuous process for cracking a hydrocarbon charge stream inthe presence of subdivided catalyst particles, wherein the hydrocarbonstream effects a fluidized contacting of the particles in a confinedreaction zone, conversion products are separated from the contactedparticles, separated catalyst particles containing a coke deposit etfectfluidized contacting of an oxygen containing stream in a separateconfined regeneration zone, combustion gas products are separated fromregenerated catalyst particles and such regenerated catalyst particleswith e reduced coke content are returned to the reaction zone forcontact with hydrocarbon charge stream, the improved method of effectingimproved product yields from the hydrocarbon charge stream by operatingto provide a high temperature level in the regeneration zone and anoverall reduction of coke yield in the process which comprises,preheating the hydrocarbon stream and Varying the catalyst circulationrate to effect a coke deposition level on the catalyst particlessuflicient to provide a temperature above 1l50 F. in the regenerationzone when oxidizing the coke on the catalyst particles in the presenceof a controlled oxygen containing stream introduced to the regenerationzone, and regulating the introduction of the oxygen containing stream tothe regeneration zone directly responsive to a predetermined temperaturedifferential between the gas outlet section and the catalyst contactingsection of the regeneration zone to minimize excess oxygen therein andto preclude after-burning in the upper portion of the regenerating zone.

3. In a continuous process for cracking a hydrocarbon charge streamcomprising fresh feed and recycle oil in the presence of subdividedcatalyst particles, wherein the hydrocarbon stream effects a uidizedcontacting of the particles in a confined reaction zone, conversionproducts are separated from the contacted particles, separated catalystparticles containing a coke deposit effect uidized contacting of anoxygen containing stream in a separate confined regeneration zone,combustion gas products are separated from regenerated catalystparticles and such regenerated catalyst particles With a reduced cokecontent are returned to the reaction zone for contact with hydrocarboncharge stream, the improved method of electing improved product yieldsfrom the hydrocarbon charge stream by operating to provide a hightemperature level in the regeneration zone and an overall reduction ofcoke yield in the process which comprises, varying the combined feedratio of fresh feed to recycle oil to increase the heavy oil contentthereof and simultaneously increasing reaction zone temperature toeffect a coke deposition level on the catalyst particles suliicient toprovide a temperature above 1150 F. in the regeneration zone whenoxidizing the coke on the catalyst particles in the presence of acontrolled oxygen containing stream introduced to such regenerationzone, and regulating the introduction of the oxygen containing stream tothe regeneration zone directly responsive to a predetermined temperaturedifferential between the gas outlet section and the catalyst contactingsection of the regeneration zone to minimize excess oxygen therein andto preclude afterburning in the upper portion of the regenerating zone.

1947, pp. 230, 232, 234 and 236.

ALPHONSO D. SULLIVAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.,3,161,583 y December 15,;1964

Jack B. Pohlenz 1t ie hereby eeebified bbeb errer eppeere in the ebevenumbered peben't requiring correction and that the said Letters Patentshould read as corrected below;

Column 8, line 43, for "4.5Xl0-6" read 4.5XIO6 line 54, for -"3.8X1v0'6"read 3.8Xl06 same column 8, line 63, fer "3.3X10-6" reed 3.3X106 Signedand sealed this 29th day of June 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. IN A CONTINUOUS PROCESS FOR CRACKING A HYDROCARBON CHARGE STREAM IN THE PRESENCE OF SUBDIVIDED CATALYST PARTICLES, WHEREIN THE HYDROCARBON STREAM EFFECTS A FLUIDIZED CONTACTING OF THE PARTICLES IN A CONFINED REACTION ZONE, CONVERSION PRODUCTS ARE SEPARATED FROM THE CONTACTED PARTICLES, SEPARATED CATALYST PARTICLES CONTAINING A COKE DEPOSIT EFFECT FLUIDIZED CONTACTING OF AN OXYGEN CONTAINING STREAM IN A SEPARATE CONFINED REGENERATION ZONE, COMBUSTION GAS PRODUCTS ARE SEPARATED FROM REGENERATED CATALYST PARTICLES AND SUCH REGENERATED CATALYST PARTICLES WITH A REDUCED COKE CONTENT ARE RETURNED TO THE REACTION ZONE FOR CONTACT WITH HYDROCARBON CHARGE STREAM, THE IMPROVED METHOD OF EFFECTING IMPROVED PRODUCT YIELDS FROM THE HYDROCARBON CHARGE STREAM BY OPERATING TO PROVIDE A HIGH TEMPERATURE LEVEL IN THE REGENERATION ZONE AND AN OVERALL REDUCTION OF COKE YIELD IN THE PROCESS WHICH COMPRISES, VARYING THE REACTION ZONE TEMPERATURE AND THE CONTACT TIME OF THE HYDROCARBON STREAM WITH THE CATALYST IN THE REACTION ZONE RESPONSIVE TO THE RREFRACTORY CHARACTERISTICS OF SAID HYDROCARBON CHARGE STREAM AND EFFECTING A COKE 